A chimneys exposure to weather will cause deterioration and need repair. Flues and brick/stone can be replaced if required. The concrete cap/top/crown is usually cracked or falling apart, and can be replaced incorporating a drip ledge to help protect the brick. Some harder brick are more durable and seem to last without the wide drip ledge. Sometimes a metal chimney cap/cover is used on top of the flue to help keep rain and animals out of the chimney, Make it look new again!